J.L.
Hi R.. I know everyone is different, but what worked for me when I despised my mom's boyfriend was when my mom and I started doing stuff together, without him. If she feels anything like I did, she feels like he is taking you away from her and that you care about him more than you do her. Maybe you could have a few girls days out and take her to the mall or a movie or something (even if it means spending a little money on her) it just might be worth it to get them closer. Also, when you are alone with her, don't talk about him right away. It will only make her upset because she will think that you would rather be with him than with her. After my mom and I started hanging out more, it made me realize that he wasn't the only person in her life and I slowly grew to accept him. I hope this helps!